Polymers of ethylene and other olefins are of major commercial appeal. These polymers have a very large number of uses, ranging from low molecular weight products for lubricants and greases, to higher molecular weight products for manufacturing fibers, films, molded articles, elastomers, etc. In most cases, the polymers are obtained by catalytic polymerization of olefins using a compound based on a transition metal. The nature of this compound has a very strong influence on the properties of the polymer, its cost and its purity. Given the importance of polyolefins, there is a permanent need to improve the catalytic systems in order to propose new systems.
A variety of homogeneous or heterogeneous catalysts for the polymerization or copolymerization of ethylene exists. Among the families that are most widely known, examples that may be mentioned include the “Ziegler”-type catalysts involving organometallic complexes of metals from groups III and IV or “Philipps”-type catalysts involving chromium complexes. However, there are also nickel-based catalysts, which have been used in particular for many years for producing cc-olefins. Certain systems also have a certain level of tolerance toward polar media.
Among the many catalytic systems presented in the literature, examples that have been described include the combination between a nickel complex, such as bis-1,5-cyclooctadiene, with benzoic acid derivatives, for instance 2-mercaptobenzoic acid or 3,5-diaminobenzoic acid (U.S. Pat. No. 3,637,636) or with chelating tertiary organophosphorus ligands (U.S. Pat. No. 3,635,937, U.S. Pat. No. 3,647,914) or alternatively with glycolic, thioglycolic or thiolactic acid (U.S. Pat. No. 3,661,803). U.S. Pat. No. 3,686,159 describes the use of a complex of nickel in oxidation state zero, such as, once again, bis-1,5-cyclooctadiene, with a phosphorus ylide ligand. The above inventions have in common the in situ formation of the active species in the polymerization medium.
Other methods, for instance in American patent U.S. Pat. No. 4,716,205 or Bulgarian patent BG 60319, claim catalytic nickel systems that may be isolated, but it is necessary to introduce into the polymerization medium an acceptor compound capable of extracting one of the ligands from the nickel complex in order to make it active. The in situ technique does not allow the catalytic system to be isolated so as to precisely identify its structure, but the procedure has the merit of being simple and it limits the manipulations of the catalysts, which is a source of contamination.
U.S. Pat. Nos. 4,293,727, 4,301,318 and 4,529,554 relate to ethylene oligomerization processes that involve placing ethylene in contact with nickel ylides comprising sulfonated substituents. These ylides especially have the drawback of being difficult to synthesize.
U.S. Pat. No. 4,716,205 relates to the polymerization of ethylene in the presence of certain nickel-containing catalysts.
In the article entitled “Ethylene Homopolymerization with P,O-Chelated Nickel Catalysts” by U. Klabunde et al., Journal of Polymer Science, Part A: Polymer Chemistry, Vol. 25, 1989–2003 (1987), and also in the article “Nickel catalysis for ethylene homo- and copolymerization” by U. Klabunde and S. D. Ittel, Journal of Molecular Catalysis, 41 (1987), 123–134, catalysts based on phosphorus and nickel are described.
The article entitled “Coordination polymerization of ethylene in water by Pd(II) and Ni(II) catalysts” by A. Held, F. M. Bauers and S. Mecking, Chem. Comm., 2000, 301–302, mentions the polymerization of ethylene in water using nitrogenous palladium (II) complexes and sulfonated nickel (II) complexes.
The French patent application published under No. 2 784 110 concerns a process for polymerizing at least one olefin in the presence of at least one catalyst comprising at least one sequence E-M-X in which E represents an oxygen or sulfur atom, M represents a nickel, palladium or platinum atom, and X represents a phosphorus, arsenic or antimony atom, in a medium comprising a continuous liquid phase which comprises more than 30% by weight of water. The catalyst example cited in said document is the structure represented by formula (1)
in which the radicals R1, R2, R3, R4 and R5, which may be identical or different, may be chosen from hydrogen, alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl radicals, halogens, the hydroxyl radical, alkoxide radicals, —C(O)OR′ in which R′ represents a hydrocarbon-based radical that may contain from 1 to 15 carbon atoms, —SO3Y in which Y is chosen from Li, Na, K, NH4⊕, NR″4⊕ in which R″ represents a hydrocarbon-based radical that may contain from 1 to 15 carbon atoms.
Also mentioned as a catalyst in said document is the structure represented by formula
in which the radicals R6, R7, R8, R9, R10, R11, R12 and R13, which may be identical or different, may be chosen from the same list of radicals as R1 to R5 above, E′-M′-X′ and E″-M″-X″ being two sequences of the type E-M-X and may be identical or different, R being a divalent hydrocarbon-based radical. The aim of the invention is to propose a novel catalyst for polymerizing olefins, which has improved activity and production efficiency, even in the presence of a polar medium, given that polar media generally considerably reduce the activity of the catalysts.
The invention also proposes to provide a catalyst that can be prepared in situ.
This catalyst corresponds to the following formula:
in which:
E is an oxygen or sulfur atom;
X is a phosphorus, arsenic or antimony atom;
M is a nickel, palladium or platinum atom comprising an unattributed valency;
a is 1 or 2;
R1, R2 and R3, which may be identical or different, may be chosen from hydrogen, alkyl, cycloalkyl, aryl, alkylaryl and arylalkyl radicals, each generally containing from 1 to 20 carbon atoms, the hydroxyl radical, alkoxide radicals (with from 1 to 20 carbon atoms), —C(O)OR′ in which R′ represents a hydrocarbon-based radical that may contain from 1 to 15 carbon atoms, —SO3Y in which Y is chosen from Li, Na, K, NH4⊕, NR″4⊕ in which R″ represents a hydrocarbon-based radical that may contain from 1 to 15 carbon atoms; and
Z represents a hydrocarbon-based radical containing 2 or 3 carbon atoms;
R represents a hydrocarbon-based radical of valency a; on condition that at least one of the radicals Z and R bears at least one electron-withdrawing substituent.
Such a catalyst thus makes it possible to obtain a polyolefin, for instance polyethylene or an ethylene copolymer, of high molecular mass, with very high activity even in the presence of a polar medium.
A subject of the invention is also a process for preparing the catalyst according to the invention, comprising the following reaction, in which L is a ligand:
in which E, X, M, Rf and R1, R2, R3 and R4 have the meanings given above.
Another subject of the present invention is a process for polymerizing at least one olefin, which involves placing said olefin(s) in contact with a catalyst according to the invention.